1. Field of the Invention
The present invention relates to a blasting charge comprising a blasting composition, e.g., a water-bearing explosive, supported within a sinuous length of semi-rigid tubing, and to a method of loading explosive into a borehole from a coil of semi-rigid tubing laden with the explosive.
2. Description of the Prior Art
Water-bearing explosives, which typically comprise an oxidizing component and a fuel component dispersed or dissolved in an aqueous medium that normally is thickened or gelled, currently are available in the form of small-diameter charges for use in underground blasting operations. The most commonly available form of charge is a cartridge comprised of a tube of plastic film, filled with explosive, and gathered at both ends and closed, e.g., by means of metal closure bands around the gathered portions. An elongated flexible charge comprised of explosive encased in plastic film also has been described.
The currently known water-bearing explosive charges frequently are not suitable for use in controlled blasting operations, e.g., in pre-shearing or pre-splitting wherein the boreholes need to be loaded with relatively light explosive charges. The required light weight necessitates the use of charge diameters generally of about 1.5 inches or less, and the difference between the charge diameter and borehole diameter may be about 0.5 inch or more. Because of the difference in these diameters, and because of the deformability or flexibility of the charges, as well as the possibility that the packaging film may rupture when high poling force is exerted during loading, it is difficult to achieve the low charge weight uniformly throughout the length of the borehole with such charges. Furthermore, the low charge weight may necessitate the use of an explosive charge having a low density, i.e., a density of less than one gram per cubic centimeter. Explosive charges of such density packaged in plastic film according to the prior art are difficult to maintain in water-containing boreholes because of the buoyancy effect of the water.